The present invention relates to a counter-current liquid-solids contactor.
A necessary and significant part of the nuclear reactor fuel cycle is the processing of nuclear fuel. Liquid-solid contacting is an element in the processing of nuclear fuel because processing requires the dissolution of various materials. Batch dissolution processes are the most commonly used. However, continuous dissolvers have advantages over batch operated dissolvers of, for example, uniformity of product, ease of control, elimination of off-gas peaks, better control of off-gas scrubbers and treatment systems, and reduced supporting equipment requirements.
An additional problem is encountered when dissolving fuel that is fabricated in rods clad in a metallic material such as stainless steel. It is desirable to remove the cladding and dissolve the fuel using as few steps as possible because of the difficulty in handling radioactive material. One method for processing such fuel, known as the shear-leach method, is to chop or shear the cladded rods into fuel pieces with the subsequent dissolution, or leaching, of the core fuel material from within the cladding. The cladding, largely inert to the dissolvent, must then be removed from the dissolver. However, no plant scale continuous dissolver for processing power reactor nuclear fuel using the shear-length method has been successfully operated to date.
The Oak Ridge National Laboratories (ORNL) have done extensive work in developing concepts for continuous dissolvers employing the shear-leach method and have designed, modeled or piloted a number of variations of continuous dissolvers. See Croenier, W. S., "Equipment for the Dissolution of Core Material from Sheared Power Reactor Fuels," ORNL-TM94, April 1971; Odom, C. H., "Continuous or Semicontinuous Leacher for Leaching Soluble Core Material from Sheared, Spent Nuclear Fuel Tubes," Proceedings of 20th Conference on Remote Systems Technology, 1972; Finney, B. C., et al, "Shear-Leach Process: Semicontinuous and Batch Leaching of Sheared, Unirradiated Stainless-Steel Clad and Zircaloy-2-Clad UO.sub.2 and UO.sub.2 -ThO.sub.2," ORNL-3984, July 1969. One type of continuous dissolver that has received considerable attention is one in which fuel passes through dissolvent located within an enclosed spiral, or Archimedes' screw. As the screw is rotated, the fuel advances through the dissolvent, eventually is raised out of the liquid and discharged.
The preferred embodiment of the present invention is a liquid-solids contactor of the Archimedes' screw type which may be used for the dissolution of nuclear fuel in a reprocessing system.